1. Field of the Invention
This invention is directed to magnetic bubble domain devices, in general, and to a one-level switch for use with magnetic bubble domain systems, in particular.
2. Prior Art
Magnetic bubble domain devices and systems are well known in the art. Currently, device, material and fabrication development is underway in order to improve operating characteristics of these bubble domain memory systems. These improvements are directed toward optimizing system organizations as well as toward increasing capacity (chip and memory) through the the use of gap tolerant propagation structures and superior fabrication techniques. Improved fabrication techniques will permit greater densities of devices, greater reliability and simplication of the fabrication processes.
One area which is the subject of much examination is the use of one-level device components including switches. To date there are only two one-level switches known. One of these switches is reported by T. J. Nelson, AIP Conference Proceedings, No. 18, Part 1, pages 95-99 (1974). In this device, a pair of opposed chevron columns are interconnected by a conductor path which passes through the apices of the chevron columns. This switch has been shown to work reasonably well in either the transfer mode or the replicate mode. However, this switch is very difficult to use in a major-minor loop chip organization inasmuch as designing a current return path compatible with the chip layout is a significant problem. While it is proposed to provide the current return path by utilization of a second gross masking process for producing another conductor layer to provide the return path, the second masking process inevitably complicates the fabrication process (relative to a one mask process) thereby resulting in lower fabrication yield. Moreover, this approach is not significantly less complicated than a two level process.
A second one level switch is proposed by Bobeck et al, IEEE Transactions on Magnetics, MAG-9, pages 474-480 (1973). In this switch, oppositely directed chevron columns are offset one from another and a pair of conductors are interconnected therebetween adjacent the ends of the respective chevron columns. While this switch has the advantage of having a current return path, it has been shown that a current required for stretching a bubble from one track to the other is far too high to be practical for a one level design. This is because the current applied to stretch a bubble from a minor loop to a major loop is divided into several paths (determined by the number of chevrons per column) thus weakening the field produced along the upper chevron. Reference is made to Kryder et al, IEEE Transactions on Magnetics, MAG-11, pages 1145-1147 (1975) for the analysis which has demonstrated the shortcomings of the Bobeck et al switch. Consequently, there are no one-level switches known in the art which are available for use in a practical major-minor loop chip organization.